1. Field of the Invention
The present invention relates to bone fixation devices, and, more particularly, to an antibiotic eluding intramedullary nail apparatus and method of fabricating an antibiotic carrier compound and applying same to the intramedullary nail. The apparatus may be used for the intramedullary fixation of fractured long bones, such as femurs, tibias, fibulas, humeri, ulnas and radii, as well as in other orthopedic and bone reconstructive procedures, such as tumors, and, in particular fractures associated with an open wound exposing surrounding soft tissue and the medullary canal of the fractured bone to bacteria and other infectious micro-organisms.
2. Background Art
Fractures of the femur, tibia, fibula, as well as humeri, ulnas and radii are common injuries the treatment of which is typically dependent upon the cause of the injury, the exact nature of the fracture, the delay in receiving treatment and the presence of, or potential for, infection. In addition, fractures in immunocompromised and bone tumor patients often require special treatment to repair and/or prevent fractures. The present invention offers an opportunity to not only treat the fracture but further may be utilized to provide supplemental treatment by dispensing antibiotic or chemotherapeutic agents.
A favored method of treatment of fractures of long bones is intramedullary fixation. Intramedullary fixation involves the use of an intramedullary nailing system wherein an intramedullary nail or rod is surgically inserted within the medullary canal of the fractured bone and held in place through the use of pins or screws inserted through the opposing ends of the intramedullary nail. Once properly inserted, the intramedullary nail will function as a mechanical strut, or splint, which facilitates the natural union of the fractured bone by minimizing forces that would otherwise disrupt the union of the fractured bone.
An alternative method of treatment relies upon the use of external fixators. Typically, stabilizing rods are positioned external to the limb and in alignment with the fractured bone. The external stabilizing rods are held in position by fastening them to fixtures secured to the fractured limb above and below the location of the fracture. Unfortunately, external fixators have the potential disadvantage of being somewhat less stable than intramedullary rods due, in part, to external fixators being weight bearing versus being weight sharing, thus sometimes permitting the bone to shift resulting in an imperfect union or nonunion of the bone at the point or points of fracture. Internal fixation devices, such as intramedullary nails, typically offer increased stability of long bone fractures.
As is quite common, fractures of long bones often result in a portion of the fractured bone actually severing a portion of the skin resulting in an "open fracture". Unfortunately, even though such intramedullary nailing techniques have been quite successful in facilitating the natural union of fractured bones, obviating the need for external fixators or internal, but open wound forms of treatment such as plates and screws, the utilization of intramedullary nails is not always an option due to the risks of morbidity, and/or mortality which can occur from bacterial infestation in tissue and bone associated with open fractures. Indeed, when fractured bones either cause, are associated with or are exposed to open wounds, bacteria and/or other forms of infectious micro-organisms are given an "open door" not only into the wound, but also into the medullary canal of the fractured bone thereby increasing the risk of the bone itself becoming infected. Contraindications for intramedullary nailing of open long bone fractures include marked delays in treatment of the injury such that significant delays are deemed per se to give rise to infection rather than merely contamination, as well as contamination which cannot be thoroughly debrided.
Accordingly, in an attempt to combat actual infections or minimize the likelihood of infection in open wound situations, several procedures have been utilized in connection with intramedullary nailing. For example, when intramedullary fixation is to be relied upon, the wounded area, as well as the medullary canal of the bone itself, are typically cleansed by radical debridement and pulsed lavage irrigation prior to insertion of the intramedullary nail. Inasmuch as such cleansing does not necessarily completely combat the existence and/or formation of bacterial infestation in these areas, perioperative antibiotic therapy is usually administered systemically for three to five days following insertion of the nail and sometimes includes the application of antibiotic irrigation at the time of surgery--all in an attempt to "reduce" the surviving population of reproducing bacterial cells that escaped debridement. Unfortunately, antibiotics are not easily administered within the medullary canal of the fractured bone after it has been set with, or without, an intramedullary nail. Accordingly, any viable bacteria can result in severe complications to the patient. In addition, the inability to apply antibiotic therapy directly to the medullary canal with ease often necessitates the use of high systemic dose applications of antibiotics presenting the risk of allergy and other reactions resulting from high dose applications of antibiotics.
One technique which has been occasionally used to inhibit and/or destroy bacteria surrounding the open wound as well as any bacteria and bacterial cells which were not destroyed during debridement, is to attempt to directly repair the fractured bone with the use of a bone cement, such as bone cement formulated from polymethlmethacrylate (PMMA), wherein the bone cement has been mixed with an antibiotic, such as gentamicin, tobramycin, erythromycin, vancomicyn, oxacillin, cloxacillin, methicillin, lincomycin, ampicillin, or colistin. The "antibiotic bone cement" mixture is occasionally applied to the fractured bone and used to "artificially" cement the fractured bone together. As the cemented bone heals, the antibiotic will exude from the bone cement for a predetermined amount of time--thus enabling some exposure of the antibiotic within the medullary canal, albeit limited to the area immediately proximate to the point of fracture.
Although the use of an antibiotic bone cement mixture has been effective in fighting bacterial infestation, there are concerns with respect to the structural integrity of the bone cement itself when the antibiotics are mixed therewith. Indeed, the utilization of too much of an antibiotic could quite conceivably result in a reduction in the tensile and compressive strength of the bone cement. Accordingly, such a condition could facilitate fatigue at the cemented region of the "repaired" bone. Additionally, the use of bone cement may potentially result in the formation of scar tissue proximate to the cemented region.
In addition to utilizing such "antibiotic bone cement" mixtures for facilitating structural cemented unity of fractured bones, such mixtures have more commonly been utilized in "non-structural" applications as well. Antibiotic cement mixtures have been formed immediately prior to surgery into beads strung together on surgical grade wire. The string of "antibiotic beads" may thus be inserted into an open wound (which may have been caused by a bone fracture, or even from an incision during surgery), wherein the desired antibiotic is capable of release from the hardened cement after such insertion. Again, such an application is limited to application of antibiotic therapy external to the medullary canal. Moreover, antibiotic beads most always must be removed from the patient due to the risk that the beads may become dislodged and migrate from the point of insertion. More importantly, there is evidence that beads remaining in soft tissue will, over time, become surrounded by dense fibrous tissue both reducing the therapeutic effect of the antibiotic as well as causing discomfort to the patient. An example of such an antibiotic cement compound bead is Gentamicinpolymethylmethacrylate ("G-PMMA"). Although such "beads" have been effective against bacteria surrounding the open wound, they are not intended for use within the medullary canal of the bone, let alone are they intended for cooperation with an intramedullary nail or other type of structural bone support device.
A further prior art use of mixtures of antibiotics and bone cement is in connection with total joint arthoplasty, e.g. hip replacement. In this prior art application, the bone cement is used primarily for its cement--structural property where the inclusion of an antibiotic serves to mitigate or fight a present infection minimizing the opportunity for infection to cause a mechanical failure of the implant.
Such uses of antibiotic cement in joint arthoplasty is apparently limited to providing antibiotic administration locally at the point of contact between the prosthesis and surrounding bone and tissue and is not intended to provide antibiotic application to areas deep within the medullary canal.